Electrophotographic process including a color masking operation

ABSTRACT

An electrophotographic process including a color masking operation comprising providing a photoconductive insulator as a main photosensitive element and a substantially transparent photoconductive insulator as a transparent photosensitive element, where the main photosensitive element is provided with a grounded conductive support and the transparent photosensitive element is provided with a transparent grounded conductive support and where the spectrum sensitivity region of the transparent photosensitive element is different from the spectrum sensitivity region of the main photosensitive element or the main photosensitive element combined with a colored filter, charging both photosensitive elements with the same polarity, facing the charged surfaces of both the photosensitive elements toward each other so that a slight gap exists therebetween (1) with the colored filter interposed and/or a substantially transparent insulator interposed, or (2) with nothing interposed, image exposing while both the photosensitive elements are held in registry from the side of the transparent photosensitive element to obtain the electrostatic latent images of reflected image relation on the main photosensitive element and the transparent photosensitive element, and developing the latent image on the main photosensitive element while maintaining the registry between both the photosensitive elements, the amount of toner deposited being influenced by the latent image on the transparent photosensitive element.

United States Patent [191 Matsumoto et al.

[ 1 Oct. 29, 1974 ELECTROPI-IOTOGRAPI-IIC PROCESS INCLUDING A COLORMASKING OPERATION Inventors: Seiji Matsumoto; Isoji Takahashi, both ofAsaka, Japan Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan Filed: Dec. 28, 1971 Appl. No.: 213,136

[30] Foreign Application Priority Data Dec. 28, 1970 Japan 45-120544 us.or. 96/1.2 Int. Cl. G03g 13/00, 003 13/06 Field of Search 96/1.2, 9

References Cited UNITED STATES PATENTS FOREIGN PATENTS OR APPLICATIONS6,812,120 3/1970 Netherlands 96/1.2

Primary Examiner-Ronald H. Smith Assistant Examiner-John R. Miller, Jr.Attorney, Agent, or Firm-J. T. Martin; Gerald J. Ferguson, Jr.; JosephJ. Baker [57] ABSTRACT An electrophotographic process including a colormasking operation comprising providing a photoconductive insulator as amain photosensitive element and a substantially transparentphotoconductive insulator as a transparent photosensitive element, wherethe main photosensitive element is provided with a grounded conductivesupport and the transparent photosensitive element is provided with atransparent grounded conductive support and where the spectrumsensitivity region of the transparent photosensitive element isdifferent from the spectrum sensitivity region of the mainphotosensitive element or the main photosensitive element combined witha colored filter, charging both photosensitive elements with the samepolarity, facing the charged surfaces of both the photosensitiveelements toward each other so that a slight gap exists therebetween l)with the colored filter interposed and/or a substantially transparentinsulator interposed, or (2) with nothing interposed, image exposingwhile both the photosensitive elements are held in registry from theside of the transparent photosensitive element to obtain theelectrostatic latent images of reflected image relation on the mainphotosensitive element and the transparent photosensitive element, anddeveloping the latent image on the main photosensitive element whilemaintaining the registry be tween both the photosensitive elements, theamount of toner deposited being influenced by the latent image on thetransparent photosensitive element.

7cm, 3 Drawing ri id;

ELECTROPIIOTOGRAPIIIC PROCESS INCLUDING A COLOR MASKING OPERATIONBACKGROUND OF THE INVENTION l. Field of the Invention The presentinvention relates to a masking process which compensates deficiencies inthe spectral absorption properties of coloring agents used for formingelectrophotography multicolor images.

2. Description of the Prior Art The so-called subtractive color processis utilized for multi-color electrophotographic printing to obtain acolored image by distributing the quantities of three kinds of coloringagents, which respectively absorb blue, green and red components ofvisible rays. In the subtractive color process, there are used threekinds of coloring agents: yellow to absorb blue; magenta to absorbgreen; and cyan to absorb red. Coloring agents of magenta and cyan, suchas printing inks, pigments, dyestuffs, etc. absorb only green or red,respectively, and they do inaccurately absorb other wave length areas.For example, cyan coloring agents absorb a fair amount of green and aminor amount of blue while magenta absorbs a fair amount of blue and aminor amount of red. The yellow coloring agent is nearly ideal inabsorption.

Accordingly to correct the inaccurate absorption of cyan coloring agentsin the image, the quantity of magenta coloring agent to absorb greendecreased by the amount of said inaccurate absorption of the cyancoloring agent. The overlapping portions of cyan and magenta coloragents will then absorb a proper amount of green. Also, the cyancoloring agent absorbs blue and, if necessary, a decrease of yellowcoloring agent corresponding to the quantity of cyan coloring agent inthe image will overcome this fault. Correction for the inaccurateabsorption of magenta coloring agents is quite the same.

SUMMARY OF THE INVENTION In the present invention, a transparentelectrophotographic sensitive element and an ordinaryelectrophotographic sensitive element are provided. The photosensitivelayers are sensitive to different regions of the spectrum. The twophotosensitive elements are uniformly charged and are placed asphotosensitive layers facing each other to obtain simultaneously twocolor separated electrostatic latent images by exposure from the side ofthe transparent photosensitive element.

For multi-color electrophotography, the operations the two colorseparated latent images face each a small and definite distance apartand developing with a coloring agent corresponding to the colorseparated latent image to be developed. This process is repeated toobtain a multi-color electrophotography print corrected for inaccurateabsorption of the coloring agents.

Thus, a primary object of the present invention is to provide a processof correcting the inaccurate absorption of coloring agents and provideclear color images.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an illustration of theexposure process of the present invention.

FIGS. 2 and 3 are illustrations of the whole process of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION The principle of the presentinvention will now be described in greater detail with reference to theaccompanying drawings.

FIG. 1 is an illustration the exposure process by the present invention.In FIG. 1, 12 is the main photosensitive element and comprises a mainphotosensitive layer 1 which is a photoconductive insulating layer, andconductive support 2. p

13 is the transparent photosensitive element which acts as a developingelectrode during development, and comprises transparent photosensitivelayer 4 which is, a photoconductive insulating layer, and transparentsupport 5.

7 represents the charge uniformly given the main photosensitive layer 1,and 8 represents the charge uniformly given the transparentphotosensitive layer 4. The uniform charge may be either positive ornegative, but the charges on the main and transparent photosensitivelayers should be the same polarity. A negative charge is shown in FIG.1.

10 is an original picture such as a color slide for exposure. 11 is asource of illumination, and 9 is a projection lens. 14 is a red, greenor blue filter inserted between the transparent photosensitive layer 4and the main photosensitive layer 1. The main photosensitive layer andthe trannsparent photosensitive layer are made to face each other, andfilter 14 is placed between them whereafter exposure is made from thetransparent photosensitive layer side as shown.

By exposure, electrostatic latent images are formed on bothphotosensitive layers. Since the transparent photosensitive layersspectral sensitivity distribution differs from that of the mainphotosensitive layer due to the combination of the filter 14 and themain photosensitive layer, the electrostatic latent images formed aredifferent and correspond to the colors of the original picture.

The total (or resulting) spectral sensitivity distribution of the mainphotosensitive layer is a function not only of the spectral sensitivityof the main photosensitive layer per se but also the spectraltransmittance of the filter 14. It is important that the total (orresulting) spectral sensitivity distribution of the main photosensitivelayer (that is, the spectral transmittance of filter 14 plus thespectral sensitivity of the main photosensitive layer) is substantiallydifferent from the spectral sensitivity of the transparentphotosensitive layer. Thus, it is possible that the spectral sensitivityof the two photosensitive layers be different or the spectralsensitivity may be the same with a filter such as filter 14 inserted.

For example, an electrostatic latent image corresponding to the magentaimage portion on the main photosensitive layer may be made as follows(where the main photosensitive layer is panchromatically sensitized): Asthetransparent photosensitive layer 4, a red sensitive layer(non-sensitive to blue and green) is used. In order to cut ultravioletradiation, it is advisable to insert an ultra-violet filter in anappropriate position between the light source 11 and the transparentphotosensitive element 13. The main photosensitive layer 1 is exposed tolight through the transparent photosensitive element 13 and the filter14 (which is a green filter and only transmits green light). Thus, onthe main photosensitive layer 1 an electrostatic latent imagecorresponding to green light, that is, the magenta portion of the imageis formed. While on the transparent photosensitive layer 4 which isred-sensitive, an electrostatic latent image corresponding to red light,that is, the cyan portion of the image is formed.

The thus obtained electrostatic latent images are then developed.

FIG. 2 is a representation of the relative positions of the elementsduring development. The main photosensitive element and the transparentphotosensitive element are secured with a small space therebetween (toinsure no movement) in a facing relationship as during exposure. 3represents the electrostatic latent image on the main photosensitivelayer and 6 represents the electrostatic latent image on the transparentphotosensitive layer. In such a state, the electrostatic latent image 3(for example, having a negative polarity) on the main photosensitivelayer is developed with a positively charged magenta toner. The coloringagent adheres well to the edge portion of electrostatic latent image 3on the main photosensitive layer 1 which does not face the electrostaticlatent image 6 on the transparent photosensitive layer as can be seen inFIG. 2. Only a portion of coloring agent, determined by the differenceof electric field strength between electrostatic latent image 3 andelectrostatic latent image 6 adheres to that portion of electrostaticlatent image 3 which faces electrostatic latent image 6 on transparentphotosensitive layer 4. Thus, it is possible to decrease the quantity oftoner which adheres to electrostatic latent image 3 by using a maskingeffect, that is by controlling the electric field of electrostaticlatent image 3 with electrostatic latent image 6.

As stated above, the latent image 6 corresponds to the cyan portion ofthe original and on the highly charged portion of the mainphotosensitive element a large amount of magenta toner is deposited. Onthe main photosensitive layer the magenta toner is depositedcorresponding to the charge, that is, the latent image. However, theamount of toner deposited is influenced by the charge on the transparentphotosensitive layer (that is, latent image 6). Therefore, the amount oftoner deposited on the portion which faces the highly charged portion ofthe latent image 6 is decreased. The magenta image density thusdecreased is compensated by the magenta absorption portion of the cyantoner image which normally is an unwanted absorption.

For reproduction of a three colored image such as a color slide, theabove process is carried out in cyan, magenta and yellow colors. Toobtain a three colored image by the use of the same main photosensitivelayer, the main photosensitive layer must be panchromaticallysensitized.

The following shows the combinations of the main photosensitive layerand filters and the spectral sensitivity of the transparentphotosensitive layer to obtain various colors:

Toner Color Spectral Sensitivity of Thus, the toner image on the mainphotosensitive layer is obtained by correcting the inaccurate absorptionof individual toner image for other colors.

'The electrostatic latent image of the transparent photosensitive layerand the main photosensitive layer should be developed with no movementin their positions while they are facced but since exposure is carriedout with one above another, registration is very easy.

For example, the photosensitive elements may be fixed relative to eachother at one end, or may have a stick inserted into holes at one corner,etc.

The two electrostatic latent images are easily formed by a one timeexposure.

The electrostatic latent images on the transparent photosensitiveelement and the main photosensitive element are in a mutual imagerelationship because the former is exposed from the support mirror sideand the latter from the photosensitive layer side.

Accordingly, if the two images are faced as they are exposed, they matchcompletely and are in a convenient form for development.

The present invention thus finds excellent application to obtainingelectrostatic latent images in a mirror image relation by a one timeexposure.

In representative photosensitive elements employed in the presentinvention, the following may be used.

For the conductive support, the following are generally used:

l. Paper having applied thereto polyvinyl alcohol, etc. so as to beelectrically conductive;

2. Plastic films having a conductive surface layer, such as vacuumvaporized metal;

3. Metallic foils;

4. Metallic plates;

5. Plastic films having applied thereto organic materials, e.g.,potassium polybenzene sulphonate so as, to be conductive.

As the main photosensitive layer, any photoconductive material may beused, for example, the following materials can be used:

I. Photoconductive zinc oxide which is spectrally sensitized by acoloring material, applied on the support in a polymeric binder, e.g., astyrenated alkyd resin, to provide a 5-30 micron dry thickness.

2. Photoconductive CdS powder which is spectrally sensitized by acoloring material absorptive in the red, green and blue regions, appliedas in 1 above with a binder.

3. Selenium or selenium/tellurium evaporated on the support to a 10-200micron thickness.

4. An organic photoconductive body such as polyvinyl carbazole which isspectrally sensitized by a coloring material, applied on the supportwith a plasticizer.

For the transparent photosensitive element, the following may be used:

For the support:

1. NESA coated glass.

2. Cu] is on a plastic film.

3. A thin metal evaporated on the plastic film which is transparent andelectrically conductive.

The transparent photosensitive part need not neces sarily be completelytransparent, and may be translucent with little absorption or diffusionof light because the main photosensitive part is exposed through thetransparent photosensitive element.

For the photosensitive layer:

2. An organic photoconductive body such as polyvinyl carbazole which isdye-sensitized.

When the main photosensitive layer is striking in color, for example, anevaporated selenium or selenium and tellurium layer, the toner image ispreferably transferred onto an appropriate material such as paper, sothat the colored image is obtained by repetitively transferring thedifferent color images on the same material in position registration,

Where the colored image deposited is transferred, main photosensitivelayers which are respectively sensitive to only blue, green and red canbe used in each transfer process. In this case of the filter 14 is notnecessary, since the spectral sensitivity of the main photoconductivelayer is only blue, green or red.

in this case two photoconductive layers can directly each other, but inorder to prevent undesirable discharging it is preferable to insert atransparent insulative material, that is, a plastic film between thesetwo photoconductive layers.

For the present invention, any of the following wellknownelectrophotographic developments can be used.

1. Cascade developing;

2. Powder cloud developing;

3. Liquid developing;

4. Magnetic brush developing.

When the colored toner image is obtained by applying toner images on thesame photosensitive material, the first toner image should not influencethe electrophotography process occurring during the formation of thesecond color toner image. Thus, the liquid developing process using finetoner dispersed in an insulating liquid as the developer is especiallysuitable in this situation.

The present invention is also available for obtaining a separatedpositive separation or negative separation with color masking forprinting instead of a colored image by applying toner image in anelectrophotography process. In the instance, there is no need to changethe color of the toner to each color with multiple applications. Theexposure and development of the present invention are made one time witheach color, and the color masked separated positives or negatives areobtained which can be used in photoengraving.

In the present invention, the foregoing description applies only toordinary color separation color reproduction. In addition, the color offilter 14 shown in FIG. I, or the spectral sensitivity of the mainphotosensitive layer combined with the filter 14, or the spectralsensitivity of the main photosensitive layer without the use of filterH, can be used to obtain special effects to extend over two colors or toselect the middle color, without being limited to red, green and blue.The spectral sensitivity of the transparent photosensitive layer mayalso be varied in the same manner.

It goes without saying that the present invention is available forobtaining images by a positive positive or negative negative process aswell as by a negative positive process.

For instance, for negative positive reproduction, the developingelectrode is given a bias voltage of the same polarity as that of thecharge of the electrostatic 6 latent image and developing is made with acharged toner of the same polarity.

The present invention, as shown in H0. 3, can employ a transparentphotosensitive element wherein the charge thereon acts as a biasingvoltage instead of a developing electrode to which is applied a biasingvoltage.

In FIG. 3, for example, for obtaining a toner image of magenta, muchmagenta toner sticks to the low charge portion 23 as compared to chargedarea 21 of the electrostatic latent image on the main photosensitiveelement 12 because the toner, being charged negative, is repelled by thecharge 20 of the transparent photosensitive layer to the mainphotosensitive part.

This is the case of reversal development. In contrast with the abovecases, toners deposit on the portion where less charge is present on themain photoconductive element. On portion 22 where the charge is lesscorresponding to the cyan image of the original, magenta toner isdeposited but reduced.

Thus, a masked image of magenta, which is in negative positive relationto the original, is obtained on the main photosensitive part.

Numerous modifications of the invention will become apparent to one ofordinary skill in the art upon reading the foregoing disclosure. Duringsuch a reading it will be evident that this invention provides a uniqueelectrophotographic process for accomplishing the objects and advantagesherein stated.

What is claimed is:

1. An electrophotographic process including a color masking operationcomprising providing a photoconductive insulator as a mainphotosensitive element and a substantially transparent photoconductiveinsulator as a transparent photosensitive element, where said mainphotosensitive element is provided with a grounded conductive supportand said transparent photosensitive element is provided with atransparent grounded conductive support and where the spectrumsensitivity region of said transparent photosensitive element isdifferent from the spectrum sensitivity region of said mainphotosensitive element or said main photosensitive element combined witha colored filter, charging both photosensitive elements with the samepolarity, facing the charged surfaces of both said photosensitiveelements toward each other so that a slight gap exists therebetween (l)with said colored filter interposed and/or a substantially transparentinsulator interposed, or (2) with nothing interposed, image exposingwhile both said photosensitive elements are held in registry from theside of said transparent photosensitive element to obtain theelectrostatic latent images of reflected image relation on said mainphotosensitive element and said transparent photosensitive element, anddeveloping the latent image on said main photosensitive element whilemaintaining said registry between both said photosensitive elements, theamount of toner deposited being influenced by the latent image on saidtransparent photosensitive element.

2. An electrophotographic process as in claim 1 where said mainphotosensitive element is panchromatic and blue, green, and red filtersare used respectively to effect a subtractive color process.

3. An electrophotographic process as in claim 1 where said mainphotoconductive material is panchromatic and a red filter is used, saidtransparent photoconductive material is red and green sensitive. and thecolor of the toner is yellow.

6. An electrophotographic process as in claim 1 where said toner is ofthe same polarity as that of said latent images whereby reversaldevelopment is effected.

7. An electrophotographic process as in claim 1 where the polarity ofsaid toner is opposite to that of said latent images to effect positivedevelopment.

1. AN ELECTROPHOTOGRAPHIC PROCESS INCLUDING A COLOR MASKING OPERATION COMPRISING PROVIDING A PHOTOCONDUCTIVE INSULATOR AS A MAIN PHOTOSENSITIVE ELEMENT AND A SUBSTANTIALLY TRANSPARENT PHOTOCONDUCTIVE INSULATOR AS A TRANSPARENT PHOTOSENSITIVE ELEMENT, WHERE SAID MAIN PHOTOSENSITIVE ELEMENT IS PROVIDED WITH A GROUNDED CONDUCTIVE SUPPORT AND SAID TRANSPARENT PHOTOSENSITIVE ELEMENT IS PROVIDED WITH A TRANSPARENT GROUNDED CONDUCTIVE SUPPORT AND WHERE THE SPECTRUM SENSITIVITY REGION OF SAID TRANSPARENT PHOTOSENSITIVE ELEMENT DIFFERENT FROM THE SPECTRUM SENSITIVITY REGION OF SAID MAIN PHOTOSENSITIVE ELEMENT OR SAID MAIN PHOTOSENSITIVE ELEMENT COMBINED WITH A COLORED FILTER, CHARGING BOTH PHOTOSENSITIVE ELEMENTS WITH THE SAME POLARITY, FACING THE CHARGED SURFACES OF BOTH SAID PHOTOSENSITIVE ELEMENTS TOWARD EACH OTHER SO THAT A SLIGHT GAP EXISTS THEREBETWEEN (1) WITH SAID COLORED FILTER INTERPOSED AND/OR A SUBSTANTIALLY TRANSPARENT INSULATOR INTERPOSED, OR (2) WITH NOTHING INTERPOSED, IMAGE EXPOSING WHILE BOTH SAID PHOTOSENSITIVE ELEMENTS ARE HELD IN REGISTRY FROM THE SIDE OF SAID TRANSPARENT PHOTOSENSITIVE ELEMENTS TO OBTAIN THE ELECTROSTATIC LATENT IMAGES OF REFLECTED IMAGE RELATION ON SAID MAIN PHOTOSENSITIVE ELEMENT AND SAID TRANSPARENT PHOTOSENSITIVE ELEMENT, AND DEVELOPING THE LATENT IMAGE ON SAID MAIN PHOTOSENSITIVE ELEMENT WHILE MAINTAINING SAID REGISTRY BEBTWEEN BOTH SAID PHOTOSENSITIVE ELEMENTS, THE AMOUNT OF TONER DEPOSITED BEING INFLUENCED BY THE LATENT IMAGE ON SAID TRANSPARENT PHOTOSENSITIVE ELEMENT.
 2. An electrophotographic process as in claim 1 where said main photosensitive element is panchromatic and blue, green, and red filters are used respectively to effect a subtractive color process.
 3. An electrophotographic process as in claim 1 where said main photoconductive material is panchromatic and a red filter is used, said transparent photoconductive material is green sensitive, and the color of the toner is cyan.
 4. An electrophotographic process as in claim 1 where said main photoconductive material is panchromatic and a green filter is used, said transparent photoconductive material is red sensitive, and the color of the toner is magenta.
 5. An electrophotographic process as in claim 1 where said main photoconductive material is panchromatic and a blue filter is used, said transparent photoconductive material is red and green sensitive, and the color of the toner is yellow.
 6. An electrophotographic process as in claim 1 where said toner is of the same polarity as that of said latent images whereby reversal development is effected.
 7. An electrophotographic process as in claim 1 where the polarity of said toner is opposite to that of said latent images to effect positive development. 